UTRAN (Universal terrestrial radio access network) is the radio access network of a UMTS, wherein the UTRAN consists of Radio Network Controllers (RNCs) and Node Bs (i.e. radio base stations). The NodeBs communicate wirelessly with mobile terminals and the RNCs control the Node Bs. The RNCs are further connected to the Core Network (CN). Evolved UTRAN (E-UTRAN) is the evolution of the UTRAN towards a high-data rate, low-latency, and packet-optimised radio access network. Further, E-UTRAN consists of interconnected eNodeBs (evolved Node Bs) that are further connected to the Evolved Packet Core network (EPC). E-UTRAN is also being referred to as Long Term Evolution (LTE) and standardized within the 3rd Generation Partnership Project (3GPP).
To allow for a wide range of user equipment (UE) implementations, different UE capabilities are specified. The UE capabilities are divided into a number of parameters, which are sent from the UE at the establishment of a connection and if/when the UE capabilities are changed during an ongoing connection. The UE capabilities may then be used by the network to select a configuration that is supported by the UE.
In 3GPP standardization of E-UTRAN radio access it has been agreed to transfer the UE radio network related capability information i.e. the UE capabilities using RRC (Radio Resource Control) signaling from the UE to the eNodeB. In order to avoid uploading the UE capabilities over the radio interface between the UE and the eNodeB each time the UE performs a transition to active state (i.e. when the UE specific context is created in the eNB) it has been agreed that the eNodeB should upload the capabilities to the EPC so that they can be stored there when the UE is in idle state. When the UE returns to active state the UE capabilities should be downloaded to the eNB. Before the UE can use the services of the network in its full extent it has to exhibit its capabilities (e.g. supported bit rates, antenna configurations, bandwidths, supported access types, etc.) to the EPC. When the EPC has knowledge of the UE capabilities the EPC can tailor transmissions in conjunction with services to said UE according to its capabilities.
Generally, UE capabilities can be classified into mainly two sets of capability categories depending on which layer of the protocol hierarchy the given capability information is related to:                Access Stratum (AS) capabilities: these are the access technology dependent parts of the capability information such as terminal power class, supported frequency band etc. The AS capabilities are needed by the eNodeB.        Non Access Stratum (NAS) capabilities: this set of capability information holds the non access specific parts of the UE capability such as supported security algorithms. The NAS capabilities are used by the EPC.        
Information on the AS part of the UE capabilities needs to be present in the eNodeB in the active state of the UE. Moreover, when a handover is made from a first eNodeB to a second eNodeB the UE capability information needs to be moved from the first eNodeB to the second eNodeB. However, for a UE in the idle state there is no need to maintain any UE information, including the UE capabilities, in the eNodeBs but only in the EPC. Thus, when a UE transits to active state again, the information of the UE, including the UE capabilities, must be recreated in the eNodeB.